Investigation On Palladium-Catalyzed Functionalization Of Alkenes

As the important chemical raw materials,olefins are widely used in the field of fine chemicals such as medicines,pesticides,spices and functional materials,which has greatly improved human living standards.Generally,olefins are tend to directly react with electrophiles or coordinate with transition metals following attracted by nucleophiles for a pair ofπ-electrons,so the studies on olefins conversion have been of continuous concern to chemists from the 1900s.In the other hand,due to unique outer electrons,transition metal palladium exhibits a wide variety of chemical properties.Palladium-catalyzed transformation of olefins has not been interrupted since Wacker reaction was reported.Furthmore,the 2010Nobel Prize in chemistry—palladium-catalyzed cross-coupling reactions push the research on palladium chemistry to the peak.Therefore,how to achieve more efficient and green transformation of olefins by palladium catalysis has become a ultimate goal,which was pursued by organic chemists.In general,the palladium-catalyzed olefin activation process is primarily achieved by nucleometalation.The specific process is that the coordination between palladium catalyst with double bond reduces the electrons cloud density of olefins,and then being attacked by nucleophiles.According to the different types of nucleophiles,the nucleopalladation included oxypalladation,aminopalladation and carbopalladation,while the in situ generated organo-palladium react with olefins by migration insertion.The favored ways of quenching the alkyl palladium(Pd^Ⅱ)species areβ-hydrogen elimination or protonolysis,in addition,alkyl palladium(Pd^Ⅱ)can also be oxidized to high-valent palladium(Pd^Ⅲ or Pd^Ⅳ)and attacked by nucleophiles,or direct reductive eliminate through transmetalation orπ-allyl palladium intermediate.Due to the diversified initiating and quenching ways by controlling reaction conditions and designing substrates,palladium-catalyzed transformations of olefins usually have diversity,which can be used to build complex functionalized molecules.In this thesis,we reviewed the progress of palladium-catalyzed difunctionalization of olefins under the different initiations,and demonstrated the significant achievements in the last several decades.In the context,we have developed palladium-catalyzed efficient transformations of olefins using“green”oxidant or synthetic strategies.See the following for details:In chapter two,we developed a palladium-catalyzed environmentally friendly dioxygenation reaction of aryl and alkyl terminal alkenes,which enabled rapid assembly of valuableα-hydroxy ketones with high atom-economy.Notably,control experiments and¹⁸O-isotope labeling experiments established that H₂O₂ played a dominant dual role in this transformation.The formation of the peroxy-bridge palladium（Ⅱ）intermediate suppressed theβ-hydrogen elimination and promotes further conversion of the alkyl palladium（Ⅱ）intermediate.In chapter three,we reported a novel palladium-catalyzed alkene diacetoxylation with O₂as sole oxidant and oxygen source,which was identified by ¹⁸O-isotope labeling studies.Control experiments suggested that bis（pinacolato）diboron（B₂pin₂）played a dominant intermediary role in the formation of C-O bond.This method performed good functional group tolerance and diastereoselectivity with moderate to excellent yields,which could be successfully applied to the late-stage modification of natural products.Moreover,an atmospheric pressure of dioxygen enhances the practicability of the protocol.In chapter four,a palladium（Ⅱ）-catalyzed hydroboration of aryl alkenes with stable and easy-to-handle B₂pin₂ under mild conditions has been developed.Acetic acid acted as the solvent and the hydrogen source,which have been identified by deuterium experiments.Notably,isomerization-hydroboration of allyl benzene derivatives was observed.As a result,a series of benzyl boronic esters were obtained in moderate to excellent yields with exclusive regioselectivity,which could prepared a variety of bioactive 1,1-diaryalkane scaffolds via the palladium-catalyzed cross-coupling reaction.In chapter five,the first example of Pd-catalyzed oxidative cyclization of allyltosylamides with acetic acid is reported.This transformation involved C-N/C-C bond formation and provided 3-pyrrolin-2-ones in a one-pot manner with easy-operation,excellent atom economy and good yields.This method is applicable to cinnamyltosylamides as well as（homo）allyltosylamides.Furthermore,nitrogen-containing heterocyclic compounds with different skeletons can be obtained under the same reaction conditions through modulating the functional groups.